Air Compressor

ABSTRACT

Provided is an air compressor improved in terms of reliability by taking into consideration of the condensation of the water vapor in the compressed air. According to the present invention, an air compressor includes: a compressor main body; a compression chamber of the compressor main body compressing sucked-in air; an oil supply port supplying a lubricating oil to the compression chamber; an oil separator separating compressed air discharged from the compression chamber and the lubricating oil from each other; oil temperature adjustment means adjusting temperature of the lubricating oil supplied to the oil supply port; control means controlling the oil temperature adjustment means; sucked-in air temperature detection means detecting temperature of the sucked-in air; and sucked-in air humidity detection means detecting humidity of the sucked-in air, wherein the oil temperature adjustment means is controlled on the basis of detection information of the sucked-in air temperature detection means and of the sucked-in air humidity detection means.

TECHNICAL FIELD

The present invention relates to an air compressor.

BACKGROUND ART

A conventional oil-cooled air compressor is disclosed, for example, in JP-2014-88876-A (Patent Document 1). The Abstract of Patent Document 1 discloses “a cooling method of a liquid injection type compressor element portion in which a liquid is injected into a compression chamber of a compressor element portion via an injection valve, the method including the step of controlling the amount of the liquid injected into the compression chamber of the compressor element portion in accordance with a specific control parameter independently of other possible adjustment devices.”

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-2014-88876-A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Generally speaking, the air in the compression chamber increases in pressure due to the compression action, and increases in temperature. Furthermore, the dew point, which is the temperature at which the water vapor in the air is condensed, also increases. Thus, when a lubricating oil at a temperature equal to or lower than the dew point is supplied to the compression chamber, the water vapor in the compressed air is condensed, resulting in deterioration in the reliability of the lubricating oil.

In the air compressor disclosed in Patent Document 1, it is possible to keep the compressed air outlet at low temperature. However, the temperature of the oil supplied to the compression chamber is not taken into consideration, so that there is a problem such as regarding the reliability of the bearing of the compressor because of generation of rust, breakage of the oil film, oxidation deteriorations of the lubricating oil, and the like due to condensation of water vapor in the compression chamber.

The present invention has been made in view of the above problem. It is an object of the present invention to provide an air compressor of high reliability by taking into consideration of the condensation of the water vapor in the compressed air.

Means for Solving the Problem

To solve the above problem, there is adopted a structure as claimed, for example, in the appended claims. The present application includes a plurality of means for solving the above problem, an example of which is an air compressor including: a compressor main body; a compression chamber of the compressor main body compressing sucked-in air; an oil supply port supplying a lubricating oil to the compression chamber; an oil separator separating compressed air discharged from the compression chamber and the lubricating oil from each other; oil temperature adjustment means adjusting temperature of the lubricating oil supplied to the oil supply port; control means controlling the oil temperature adjustment means; sucked-in air temperature detection means detecting temperature of the sucked-in air; and sucked-in air humidity detection means detecting humidity of the sucked-in air, wherein the oil temperature adjustment means is controlled on the basis of detection information of the sucked-in air temperature detection means and of the sucked-in air humidity detection means.

Effect of the Invention

According to the present invention, the air compressor is operated on the basis of the temperature and humidity of the sucked-in air, so that it is possible to suppress or mitigate the condensation of the water vapor in the compressed air, making it possible to provide an air compressor of high reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the structure of an air compressor according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating the control of the air compressor according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating the operation mode of the air compressor according to the embodiment of the present invention.

FIG. 4 is a time chart illustrating the control condition of the air compressor according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating the relationship between the dew point and pressure of compressed air.

FIG. 6 is a diagram illustrating the structure of an air compressor according to a second embodiment of the present invention.

FIG. 7 is a flowchart illustrating the control of the air compressor according to the second embodiment of the present invention.

FIG. 8 is a diagram illustrating the structure of an air compressor according to a third embodiment of the present invention.

FIG. 9 is a flowchart illustrating the control of the air compressor according to the third embodiment of the present invention.

FIG. 10 is a diagram illustrating the structure of an air compressor according to a fourth embodiment of the present invention.

FIG. 11 is a flowchart illustrating lubricating oil temperature control for the air compressor according to the fourth embodiment of the present invention.

MODES FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention will be described with reference to the drawings as appropriate.

Embodiment 1

In the following, the first embodiment of the present invention will be described with reference to FIGS. 1 through 5.

FIG. 1 is a diagram illustrating the structure of the air compressor of the present embodiment. As depicted in FIG. 1, an air compressor 1 includes a compressor main body 10, an oil separator 20 separating oil, a discharged air cooling heat exchanger 21 cooling discharged air, an oil cooling heat exchanger 22 cooling the lubricating oil, and an revolution speed variable blower 23 sending air to the discharged air cooling heat exchanger 21 and the oil cooling heat exchanger 22.

The air compressor 1 sucks atmospheric air into a compression chamber 10 a of the compressor main body 10 and compresses the air to generate high-temperature/high-pressure air (for example, at approximately 80° C. and 0.8 MPa). The compressor main body 10 includes a revolution speed variable motor 10 b, and a bearing portion 10 c for the shaft transmitting the power of the motor 10 b. The bearing portion 10 c includes a bearing portion oil supply port 10 d, and the compression chamber 10 a includes a compression chamber oil supply port 10 e, with lubricating oil being supplied to them. The compressed air is discharged together with the lubricating oil, and reaches the oil separator 20 via a discharge flow path 24 (the flow path indicated by a thick solid line in FIG. 1), with the air and oil being separated from each other. Incidentally, it is not always necessary for the air and oil to be completely separated from each other. Oil of a predetermined value or less may be mixed with the air. The air from which the oil has been separated enters an air flow path 25 (the flow path indicated by a thin solid line in FIG. 1), and reaches the discharged air cooling heat exchanger 21. In the discharged air cooling heat exchanger 21, the compressed air undergoes heat exchange with the atmosphere due to an airflow 50 formed through the driving of the blower 23 (the airflow indicated by the arrow in FIG. 1), and is cooled to the use temperature region before being sent to the exterior of the air compressor 1.

On the other hand, the lubricating oil separated by the oil separator 20 (in the present embodiment, an oil for an ordinary air compressor is used) enters an oil flow path 26 (the flow path indicated by the chain-dotted line in FIG. 1), and reaches the oil cooling heat exchanger 22. At the oil cooling heat exchanger 22, the lubricating oil undergoes heat exchange with the atmosphere due to the airflow formed by the driving of the blower 23, and is cooled before being supplied to the bearing portion 10 c and the compression chamber 10 a from the bearing portion oil supply port 10 d and the compression chamber oil supply port 10 e.

The air compressor 1 of the present embodiment includes a sucked-in air temperature sensor 31 detecting the temperature (T1) of the sucked-in air and a sucked-in air humidity sensor 32 detecting the humidity (H1) of the sucked-in air, and is connected to a control board (control means) (not depicted) on which a CPU, memories such as ROM and RAM, an interface circuit, etc. are mounted. The turning ON/OFF and rotational speed control of the motor 10 b of the compressor main body 10 and the turning ON/OFF and rotational speed control of the blower 23 are performed with the control means on the basis of a program previously mounted in the ROM.

FIG. 2 is a flowchart illustrating the lubricating oil temperature control of the air compressor according to the present embodiment. This flowchart is executed as a sub routine of a main program (not depicted) controlling the operations of the air compressor 1 as a whole.

In the air compressor 1 of the present embodiment, the temperature of the lubricating oil supplied to the compression chamber oil supply port 10 e is controlled by the control flow depicted in FIG. 2. More specifically, the sucked-in air temperature T1 and the sucked-in air humidity H1 are first detected (step S101). Subsequently, an operation mode (described below) is selected on the basis of the sucked-in air temperature T1 and the sucked-in air humidity H1 detected (step S102). Next, it is determined whether or not the current operation mode and the selected operation mode coincide with each other (step S103). In the case where the operation modes coincide with each other (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program. On the other hand, in the case where the operation modes do not coincide with each other (No), the mode is changed to the operation mode selected in step S102, and the lubricating oil temperature control processing is ended, with the procedure returning to the main program.

FIG. 3 is a diagram illustrating the operation mode of the air compressor of the present embodiment. As depicted in FIG. 3, in the air compressor 1 of the present embodiment, the operation mode is selected on the basis of the sucked-in air temperature T1 and the sucked-in air humidity H1. In the case where both the sucked-in air temperature T1 and the sucked-in air humidity H1 are high, there is selected “mode 1” in which the compressor main body 10 is driven at low speed and in which the blower 23 is driven at low speed. In the case where the sucked-in air temperature T1 is low and where the sucked-in air humidity H1 is high, there is selected “mode 2” in which the compressor main body 10 is driven at high speed and in which the blower 23 is driven at low speed. In the case where the sucked-in air humidity H1 is low irrespective of the sucked-in air temperature T1, there is selected “mode 3” in which the compressor main body 10 is driven at high speed and in which the blower 23 is driven at high speed.

Incidentally, in the air compressor 1 of the present embodiment, the sucked-in air temperature T1 is regarded as a high temperature when it is 30° C. or more and is regarded as a low temperature when it is less than 30° C. The sucked-in air humidity H1 is regarded as a high humidity when it is a relative humidity of 80% or more and is regarded as a low humidity when it is a relative humidity of less than 80%. The compressor main body 10 (the motor 10 b) is driven at 6000 min⁻¹ at the time of high speed operation, and at 4000 min⁻¹ at the time of low speed operation. The blower 23 is driven at 2000 min⁻¹ at the time of high speed operation and at 1000 min⁻¹ at the time of low speed operation. Incidentally, the sucked-air temperature of 30° C. and the humidity of 80% selected as the reference are merely given examples taking into account of the actual use environment, and any restrictions are not particularly imposed.

FIG. 4 is a time chart illustrating the control condition of the air compressor of the present embodiment. As depicted in FIG. 4, before time t1, the sucked-in air temperature T1 is higher than a threshold value Tth (Tth=30° C. in the air compressor 1 of the present embodiment), and the sucked-in air humidity H1 is lower than a threshold value Hth (Hth=80% (relative humidity) in the air compressor 1 of the present embodiment), so that “mode 3” is selected for the operation, and the lubricating oil temperature is kept at a low temperature. At time t1, the sucked-in air temperature T1 is maintained in the high temperature state, but the humidity has reached Hth, so that “mode 2,” in which the sucked-in air temperature T1 is high and in which the sucked-in air humidity H1 is high, is selected as the operation mode (step S102 of FIG. 2), with the operation being switched to “mode 2” (step 103 and step 104). As depicted in the upper portion of FIG. 4, due to the switching of the operation to “mode 2,” the heat exchange amount at the oil cooling heat exchanger 22 is reduced, so that the lubricating oil temperature increases.

The lubricating oil supplied to the compressor main body 10 is heated by the frictional heat of the compression mechanism of the compressor main body 10 and the heat from the air increased in temperature through compression, whereby the lubricating oil is increased in temperature and discharged. The degree of the increase in the temperature of the lubricating oil depends upon the rotational speed (revolution speed) of the compressor main body 10. When the same oil supply condition is the same, the higher the speed (high revolution speed), the greater the degree of the increase in temperature. On the other hand, the lubricating oil increased in temperature in the compressor main body 10 is separated at the oil separator 20, and is then cooled by the oil cooling heat exchanger 22. The degree of this cooling depends upon the rotational speed (high revolution speed) of the blower 23, in other words, the amount of air blown. The higher the speed (high revolution speed), the more promoted is the cooling (the reduction in temperature). That is, the temperature of the lubricating oil supplied to the compressor main body 10 from the compression chamber 10 a is controlled by the compressor main body (the first oil temperature adjustment means) 10 and the blower (the second oil temperature adjustment means) 23. Incidentally, in the case where the blower 23 rotates at a fixed speed, the air blowing amount may be adjusted through the control of the amount of air introduced into the compressor main body 10 by a valve or the like.

FIG. 5 is a diagram illustrating the temperature vary and the vary in dew point in the case where the sucked-in air (which is here air at 30° C. at the atmospheric pressure) undergoes adiabatic compression. As indicated by the broken line in FIG. 5, when air at 30° C. undergoes adiabatic compression under the atmospheric pressure (0.1 MPa) to 0.8 MPa, the temperature rises to approximately 275° C. At this time, the dew point also increases. For example, as depicted in FIG. 5, in the case of air which is at 30° C. and of a relative humidity of 50% under the atmospheric pressure, the dew point rises from approximately 18° C. to approximately 57° C., and in the case of air which is at 30° C. and of a relative humidity of 95%, the dew point rises from approximately 29° C. to approximately 71° C. In this way, even if the temperature of the sucked-in air is the same, the higher the humidity, the higher the dew point in the compression process. Thus, when a lubricating oil at the dew point temperature or less is supplied to the compression chamber 10 a, the water vapor in the compressed air is condensed, which leads to factors of deterioration in the reliability such as generation of rust, breakage of the oil film, and oxidation deteriorations of the lubricating oil.

Thus, in the air compressor 1 of the present embodiment, the sucked-in air temperature T1 and the sucked-in air humidity H1 are detected, and, on the basis of the detection information, the oil temperature adjustment means (the revolution speed of the compressor main body 10 and the air blowing amount of the blower 23 in the present embodiment) is controlled. As a result, it is possible to ascertain the state in which deterioration in reliability is likely to occur due to condensation of the water vapor in the compressed air and to control the oil temperature adjustment means, so that it is possible to provide an air compressor with high reliability, that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like.

In the air compressor 1 of the present embodiment, there are provided two oil temperature adjustment means: the compressor main body (the first oil temperature adjustment means) 10, and the blower (the second oil temperature adjustment means) 23 sending air to the oil cooling heat exchanger 22. As a result, it is possible to realize finer control and to provide an air compressor with high reliability, that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like.

Further, in the air compressor 1 of the present embodiment, in the case where the sucked-in air temperature T1 is substantially fixed, the oil temperature adjustment means (the rotational speed of the compressor main body 10 and the rotational speed of the blower 23) is controlled such that the temperature of the lubricating oil rises as the sucked-in air humidity H1 rises (the operation mode is switched from mode 3 to mode 1 or from mode 3 to mode 2). As a result, this fact leads to an air compressor with high reliability, that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like due to condensation of water vapor in the compressed air.

Further, in the air compressor 1 of the present embodiment, in the case where the sucked-in air humidity (relative humidity) H1 is substantially fixed, the oil temperature adjustment means (the rotational speed of the compressor main body 10 and the rotational speed of the blower 23) is controlled such that the temperature of the lubricating oil rises as the sucked-in air temperature T1 rises (the operation mode is switched from mode 2 to mode 1). As a result, this fact leads to an air compressor with high reliability, that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like due to condensation of water vapor in the compressed air.

Embodiment 2

In the following, the second embodiment of the present invention will be described with reference to FIGS. 6 and 7. The components that are of the same function as those of the first embodiment are indicated by the same reference signs, and a redundant description thereof will be omitted.

FIG. 6 is a diagram illustrating the structure of the air compressor according to the second embodiment. As depicted in FIG. 6, the air compressor 1 of the present embodiment is includes an oil temperature sensor 34 in the route from the oil cooling heat exchanger 22 to the compression chamber oil supply port 10 e. Further, the air compressor 1 includes an revolution speed variable blower 23 a for sending air to the discharged air cooling heat exchanger 21, and an revolution speed variable blower 23 b (oil temperature adjustment means) for sending air to the oil cooling heat exchanger 22, and controls the blowers independently. An airflow 50 a (the airflow upward from the right in FIG. 6 as indicated by an arrow) is formed in the discharged air cooling heat exchanger 21 through the driving of the blower 23 a, and an airflow 50 b (the airflow downward from the right in FIG. 6 as indicated by another arrow) is formed in the oil cooling heat exchanger 22 through the driving of the blower 23 b.

FIG. 7 is a flowchart illustrating the lubricating oil temperature control for the air compressor of the second embodiment. This flowchart is executed as a sub routine of a main program (not depicted) controlling the operations of the air compressor 1 as a whole.

The air compressor 1 of the present embodiment controls the temperature of the lubricating oil supplied to the compression chamber oil supply port 10 e through the control flow depicted in FIG. 7. As depicted in FIG. 7, the air compressor 1 of the present embodiment detects the sucked-in air temperature T1 and the sucked-in air humidity H1 (step S201), and, based on the detection information, calculates a lubricating oil target temperature Tgoal (step S202). In the air compressor 1 of the present embodiment, the dew point temperature (Tsat) under the pressure of the position where the compression chamber oil supply port 10 e is installed is calculated (estimated) to set as the lubricating oil target temperature Tgoal. For example, by adding a safety constant (ΔT), the lubricating oil target temperature Tgoal is calculated as follows: Tgoal=Tsat+ΔT.

Next, it is determined whether or not the difference between the lubricating oil temperature T3 and the target temperature Tgoal is less than 5° C. (step S203). When step S203 holds true (Yes), it is subsequently determined whether or not the difference between the lubricating oil temperature T3 and the target temperature Tgoal is more than 2° C. (step S204). When step S204 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program. The reference temperature of 5° C. in step S203 and that of 2° C. in step S204 are merely given examples, and any restrictions are not particularly imposed

When step S203 does not hold true (No), it is subsequently determined whether or not the revolution speed of the blower 23 b has reached the upper limit revolution speed (step S250). It should be noted that in the air compressor 1 of the present embodiment, the upper limit revolution speed of the blower 23 b is 3000 min⁻¹. In the case where it is determined in step S250 that the revolution speed of the blower 23 b has reached the upper limit (Yes), it is subsequently determined whether or not the revolution speed of the compressor main body 10 (motor 10 b) has reached the lower limit revolution speed (step S251). It should be noted that in the air compressor 1 of the present embodiment, the lower limit revolution speed of the compressor main body 10 is 2000 min⁻¹. In the case where it is determined in step S251 that the revolution speed of the compressor main body 10 has reached the lower limit revolution speed (Yes), the air compressor 1 stops the operation (i.e., stops the compressor main body 10, and the blowers 23 a and 23 b) (step S252), and ends the lubricating oil temperature control processing, and the procedure returns to the main program. In this case, since high external air temperature are to be assumed, notification of abnormality or the like is effected. Incidentally, the upper limit revolution speed of 3000 min⁻¹ of the blower 23 b and the lower limit revolution speed of 2000 min⁻¹ of the compressor main body 10 (motor 10 b) are merely given examples, and any restrictions are not particularly imposed.

In the case where it is determined in step S251 that the revolution speed of the compressor main body 10 has not reached the lower limit revolution speed (No), the revolution speed of the compressor main body 10 is reduced (step S253), and the procedure returns to step S203. In the case where it is determined in step S250 that the revolution speed of the blower 23 b has not reached the upper limit (No), the revolution speed of the blower 23 b is increased (step S254), and the procedure returns to step S203.

In the case where step S204 does not holds true (No), it is subsequently determined whether or not the blower 23 b is at rest (step S260). When step S260 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program. In the case where step S260 does not hold true (No), the revolution speed of the blower 23 b is reduced (step S261), and the procedure returns to step S204. It should be noted that in the air compressor 1 of the present embodiment, the lower limit revolution speed of the blower 23 b is 500 min⁻¹. In the case where the lower limit revolution speed of the blower 23 b is 500 min⁻¹ in step S260, the blower 23 b stops in step S261. Incidentally, the lower limit revolution speed of 500 min⁻¹ of the blower 23 b is a merely given example, and any restrictions are not particularly imposed.

It is to be noted that in the air compressor 1 of the present embodiment, the operation amount in steps S253, S254, and S261 is obtained by multiplying the deviation of the lubricating oil temperature T3 and the target temperature Tgoal and the time quadrature of the deviation of the lubricating oil temperature T3 and the target temperature Tgoal by a predetermined constant.

As described above, the air compressor 1 of the present embodiment detects lubricating oil temperature T3 together with the sucked-in air temperature T1 and the sucked-in air humidity H1 to control temperature of the lubricating oil. As a result, it is possible to control the lubricating oil temperature T3 more finely, thereby providing an air compressor with high reliability that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like due to condensation of water vapor in the compressed air.

The air compressor 1 of the present embodiment is includes the blower 23 a for sending air to the discharged air temperature cooling heat exchanger 21, and the blower 23 b (the oil temperature adjustment means) for sending air to the oil cooling heat exchanger 22. The air compressor 1 can control the sending of air to the discharged air temperature cooling heat exchanger 21 and the sending of air to the oil cooling heat exchanger 22 independently. As a result, it is easy to establish compatibility between the temperature control for cooling the discharged air to a desired temperature range and the temperature control of the lubricating oil. This fact promises an air compressor with high reliability, that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like due to condensation of water vapor in the compressed air.

The air compressor 1 of the present embodiment includes the step of calculating the lubricating oil target temperature Tgoal on the basis of the sucked-in air temperature T1 and the sucked-in air humidity H1 (step S202), the step of comparing the lubricating oil temperature T3 and the lubricating oil target temperature Tgoal with each other (steps S203 and S204), and the step of controlling the lubricating oil temperature control means so as to eliminate the deviation of the lubricating oil temperature T3 and the lubricating oil target temperature Tgoal (steps S252, S253, S254, and S261). As a result, in the case where the sucked-in air temperature T1 and the sucked-in air humidity H1 vary, the lubricating oil temperature T3 can follow in accordance with the lubricating oil target temperature Tgoal more finely. This fact leads to an air compressor with high reliability, that is hard to generate rusts, breakages of the oil film, oxidation deteriorations of the lubricating oil, and the like due to condensation of water vapor in the compressed air.

In the air compressor 1 of the present embodiment, in the case where the lubricating oil temperature T3 is higher than the lubricating oil target temperature Tgoal by a predetermined value or more (step S203), control is performed so as to raise the revolution speed of the blower 23 b (step S254) or so as to lower the revolution speed of the compressor main body 10 (step S253). As a result, it is possible to lower the lubricating oil temperature, thereby ensuring the reliability through suppression or reduction in condensing water vapor while promoting the cooling of the air in the compression process. Accordingly, the efficiency of the compressor can be enhanced.

The air compressor 1 of the present embodiment defines the dew point temperature under the pressure at the position where the compression chamber oil supply port 10 e is installed as the lubricating oil target temperature Tgoal. As depicted in FIG. 5, the dew point temperature of the air rises in the compression process, so that the dew point temperature differs depending upon the pressure of the position where the compression chamber oil supply port is installed. In view of this, in the air compressor 1 of the present embodiment calculates (estimates) the dew point temperature at the position where the compression chamber oil supply port 10 e is installed, and defines the dew point temperature as the lubricating oil target temperature Tgoal. Whereby more reliable suppression in condensing the water vapor can be realized. This fact provides an air compressor with high reliability that is hard to generate rusts, breakages of the oil film, deteriorations due to oxidation of the lubricating oil, and the like.

Embodiment 3

In the following, the third embodiment of the present invention will be described with reference to FIGS. 8 and 9. The components that are of the same function as those of the first and second embodiments are indicated by the same reference signs, and a redundant description thereof will be omitted.

FIG. 8 is a diagram illustrating the structure of the air compressor of the third embodiment. As depicted in FIG. 8, the air compressor 1 of the present embodiment includes, on the downstream side of the oil separator 20, a flow path 26 a toward the oil cooling heat exchanger 22, and a bypass flow path 26 b through which no lubricating oil flows toward the oil cooling heat exchanger 22, these paths branching off. The lubricating oil having entered the flow path 26 a is cooled at the oil cooling heat exchanger 22, and then joins the lubricating oil which flows through the bypass flow path 26 b and is not cooled at the oil cooling heat exchanger 22. The bypass flow path 26 b includes an oil flow rate control valve 51 controlling the flow rate of the lubricating oil. Depending on the opening degree of the oil flow rate control valve 51, the ratios of the flow rate flowing through the bypass flow path 26 b and the flow rate flowing through the oil cooling heat exchanger 22 are controlled. In the oil cooling heat exchanger 22 and the discharged air cooling heat exchanger 21, there is formed an airflow through the driving of the blower 23. Apart from the oil flow rate control valve 51, a pump or the like may be adopted to control the flow rate of the lubricating oil.

Due to the above structure, the cooling amount of the lubricating oil at the oil cooling heat exchanger 22 is controlled by the compressor main body (the first oil temperature control means) 10 and the air blowing amount of the blower (the second oil temperature control means) 23. At the same time, it can be controlled through the opening degree of the oil flow rate control valve (the third oil temperature control means) 51. When the opening degree of the oil flow rate control valve 51 is high, the flow rate in the bypass flow path 26 b increases, and the flow rate in the oil cooling heat exchanger 22 relatively decreases, whereby the heat exchange amount decreases, and the lubricating oil temperature T3 (the detection value at the oil temperature sensor 34) after the joining rises. The flow rate control valve 51 in the air compressor 1 of the present embodiment is a butterfly valve the opening degree of which can be freely adjusted by a stepping motor. Apart from this, it is possible to adopt all manner of other well-known valves as the oil flow rate control valve 51, such as a needle type valve and a solenoid valve, so long as they are of a structure allowing the adjustment of the flow rate.

FIG. 9 is a flowchart illustrating the lubricating oil temperature control in the air compressor of the third embodiment. This flowchart is executed as a sub routine of a main program (not depicted) for controlling the operation of the air compressor 1 as a whole.

In the air compressor 1 of the present embodiment, the temperature of the lubricating oil supplied to the compression chamber oil supply port 10 e is controlled by the control flow depicted in FIG. 9. As depicted in FIG. 9, the air compressor 1 of the present embodiment detects the sucked-in air temperature T1 and the sucked-in air humidity H1 (step S301), and, based on the detection information, calculates the lubricating oil target temperature Tgoal (step S302). The air compressor 1 of the present embodiment calculates the dew point temperature under the discharge pressure of the compressor main body 10 in the case where adiabatic compression is supposed, and defines the dew point temperature as the lubricating oil target temperature Tgoal. Next, it is determined whether or not the difference between the lubricating oil temperature T3 and the target temperature Tgoal is less than 5° C. (step S303). In the case where step S303 holds true (Yes), it is subsequently determined whether or not the difference between the lubricating oil temperature T3 and the target temperature Tgoal is more than 2° C. (step S304). In the case where step S304 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program.

In the case where step S303 does not hold true (No), it is subsequently determined whether or not the valve 51 is totally closed (step S350). In the case where step S350 holds true (Yes), it is subsequently determined whether or not the revolution speed of the blower 23 has reached the upper limit revolution speed (step S351). It should be noted that in the air compressor 1 of the present embodiment, the upper limit revolution speed of the blower 23 is 3000 min⁻¹. In the case where step S351 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program. When the air blowing amount of the blower 23 is controlled, not only the heat exchange amount of the oil cooling heat exchanger 22 but also that of the discharged air cooling heat exchanger 21, that is, the discharged air temperature, may be affected. In view of this, in the present embodiment, the opening degree of the valve 51 is adjusted, and then the air blowing amount of the blower 23 is adjusted.

In the case where it is determined in step S351 that the revolution speed of the blower 23 has not reached the upper limit revolution speed (No), the revolution speed of the blower 23 is increased (step S352), and the procedure returns to step S303. In the case where it is determined in step S350 that the valve 51 is not totally closed (No), the opening degree of the valve 51 is reduced (step S353), and the procedure returns to step S303.

In the case where step S304 does not hold true (No), it is subsequently determined whether or not the valve 51 is totally open (step S360). In the case where step S360 holds true (Yes), it is subsequently determined whether or not the revolution speed of the blower 23 has reached the lower limit revolution speed (step S361). It should be noted that in the air compressor 1 of the present embodiment, the lower limit revolution speed of the blower 23 is 500 min⁻¹. In the case where step S361 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program.

In the case where it is determined in step S361 that the revolution speed of the blower 23 has not reached the lower limit revolution speed (No), the revolution speed of the blower 23 is reduced (step S362), and the procedure returns to step S304. In the case where it is determined in step S360 that the valve 51 is not totally open (No), the opening degree of the valve 51 is increased (step S363), and the procedure returns to step S304.

In the air compressor 1 of the present embodiment, the operation amount in steps S352, S353, S362, and S363 is obtained by multiplying the deviation of the lubricating oil temperature T3 and the target temperature Tgoal and the time quadrature of the deviation of the lubricating oil temperature T3 and the target temperature Tgoal by a predetermined constant.

As described above, in the air compressor 1 of the present embodiment, the lubricating oil temperature T3 is controlled by increasing and decreasing the amount of oil flowing through the oil cooling heat exchanger 22. That enables the heat exchange capacity of the oil cooling heat exchanger 22 to be adjusted easily, whereby a desired lubricating oil temperature can be obtained easily. Accordingly, more reliable suppression in condensing the water vapor can be realized. This fact provides an air compressor with high reliability that is hard to generate rusts, breakages of the oil film, deteriorations due to oxidation of the lubricating oil, and the like.

Embodiment 4

In the following, the fourth embodiment of the present invention will be described with reference to FIGS. 10 and 11. The components that are of the same function as those of the first through third embodiments are indicated by the same reference signs, and a redundant description thereof will be omitted.

FIG. 10 is a diagram illustrating the structure of the air compressor according to the fourth embodiment. As depicted in FIG. 10, the air compressor 1 of the present embodiment includes an oil flow rate control valve 51 on the downstream side of the oil separator 20. The oil flow rate control valve 51 is a three-way valve including an inlet 51 a and outlets 51 b and 51 c, and can be controlled to be placed in three states: a state (state A) in which both the outlets 51 b and 51 c are open, a state (state B) in which the outlet 51 b is open and in which the outlet 51 c is closed, and a state (state C) in which the outlet 51 b is closed and in which the outlet 51 c is open. The outlets 51 b and 51 c of the oil flow rate control valve 51 are respectively connected to a flow path 26 a and a flow path 26 b, and the flow path 26 a and the flow path 26 b are respectively connected to a flow path extending through a part 22 a of the oil cooling heat exchanger 22 and a flow path extending through the remaining part 22 b thereof. The air side heat transfer area of the part 22 a of the oil cooling heat exchanger 22 is larger than that of the remaining part 22 b of the oil cooling heat exchanger 22. Further, the outlet of the part 22 a and the outlet of the remaining part 22 b of the oil cooling heat exchanger 22 are respectively connected to a flow path 26 c and a flow path 26 d, and join together at a connection portion 26 e.

In the case where the oil flow rate control valve 51 is controlled to state A, the lubricating oil flows through both the part 22 a and the remaining part 22 b of the oil cooling heat exchanger 22, so that heat exchange is effected between the oil cooling heat exchanger 22 as a whole and the air, resulting in a reduction in temperature. In the case where the oil flow rate control valve 51 is controlled to state B, the lubricating oil flows solely through the part 22 a of the oil cooling heat exchanger 22. In the case where the oil flow rate control valve 51 is controlled to state C, the lubricating oil flows solely through the remaining part 22 b of the oil cooling heat exchanger 22. As compared with state A, in which heat exchange is effected between the oil cooling heat exchanger 22 as a whole and the air, in state B and state C, the heat exchange amount is smaller, so that the reduction in the temperature of the lubricating oil is smaller. Further, the air side heat transfer area of the part 22 a of the oil cooling heat exchanger 22 is larger than that of the remaining part 22 b of the oil cooling heat exchanger 22, so that the heat exchange amount is larger (the temperature reduction is larger) in state B than in state C.

From the above discussion, the magnitude relationship of the heat exchange amount in the control state of the oil flow rate control valve 51 is as follows: state A>state B>state C. Under the same air blowing condition, the lubricating oil temperature T3 is lowest in state A and highest in state C.

FIG. 11 is a flowchart illustrating the lubricating oil temperature control in the air compressor of the fourth embodiment. This flowchart is executed as a sub routine of a main program (not depicted) controlling the operation of the air compressor 1 as a whole.

The air compressor 1 of the present embodiment controls the temperature of the lubricating oil supplied to the compression chamber oil supply port 10 e through the control flow depicted in FIG. 11. As depicted in FIG. 11, the air compressor 1 of the present embodiment detects the sucked-in air temperature T1 and the sucked-in air humidity H1 (step S401), and, based on the detection information, calculates the lubricating oil target temperature Tgoal (step S402). In the air compressor 1 of the present embodiment, the dew point temperature at the discharge pressure of the compressor main body 10 in the case where adiabatic compression is assumed is calculated as the lubricating oil target temperature Tgoal. Next, it is determined whether or not the difference between the lubricating oil temperature T3 and the target temperature Tgoal is less than 5° C. (step S403). In the case where step S403 holds true (Yes), it is subsequently determined whether or not the difference between the lubricating oil temperature T3 and the target temperature Tgoal is more than 2° C. (step S404). In the case where step S404 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program.

In the case where step S403 does not hold true (No), it is subsequently determined whether or not the valve 51 is in state A (in which the outlet 51 b is open and in which the outlet 51 c is open) (step S450). In the case where step S450 holds true (Yes), it is subsequently determined whether or not the revolution speed of the blower 23 has reached the upper limit revolution speed (step S451). In the case where step S451 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program.

In the case where it is determined in step S451 that the revolution speed of the blower 23 has not reached the upper limit revolution speed (No), the revolution speed of the blower 23 is increased (step S452), and the procedure returns to step S403. In the case where it is determined in step S450 that the valve 51 is not in state A (No), it is subsequently determined whether or not the valve 51 is in state B (in which the outlet 51 b is open and in which the outlet 51 c is closed) (step S453), and in the case where step S453 holds true (Yes), the valve 51 is controlled to state A (step S454), and the procedure returns to step S403. In the case where step S453 does not hold true (No), the valve 51 is controlled to state B (step S455), and the procedure returns to step S403.

In the case where step S404 does not hold true (No), it is subsequently determined whether or not the valve 51 is in state C (in which the outlet 51 b is closed and in which the outlet 51 c is open) (step S460). In the case where step S460 holds true (Yes), it is subsequently determined whether or not the revolution speed of the blower 23 has reached the lower limit revolution speed (step S461). In the case where step S461 holds true (Yes), the lubricating oil temperature control processing is ended, and the procedure returns to the main program.

In the case where it is determined in step S461 that the revolution speed of the blower 23 has not reached the lower limit revolution speed (No), the revolution speed of the blower 23 is reduced (step S462), and the procedure returns to step S404. In the case where it is determined in step S460 that the valve 51 is not in state C (No), it is subsequently determined whether or not the valve 51 is in state B (step S463), and in the case where step 463 holds true (Yes), the valve 51 is controlled to state C (step S464), and the procedure returns to step S404. In the case where step S463 does not hold true (No), the valve 51 is controlled to state B (step S465), and the procedure returns to step S404.

As described above, in the air compressor 1 of the present embodiment, the lubricating oil temperature T3 is controlled by controlling the condition of the lubricating oil flowing within the oil cooling heat exchanger 22. That enables the heat exchange capacity of the oil cooling heat exchanger 22 to be adjusted easily, whereby a desired lubricating oil temperature can be obtained easily. Accordingly, more reliable suppression in condensing the water vapor can be realized. This fact provides an air compressor with high reliability that is hard to generate rusts, breakages of the oil film, deteriorations due to oxidation of the lubricating oil, and the like.

While in the present embodiment there is adopted as the oil flow rate control valve 51 a three-way valve two outlets of which can be opened and closed, it is also possible to form the flow rate control valve 51 through a combination of a plurality of opening/closing valves or to adopt a valve allowing switching of the opening degree in many stages, thereby controlling more finely.

The present invention is not restricted to the embodiments described above but includes various modifications. For example, while the control in the air compressor of the first embodiment is performed so as to switch between three operation modes, it is also possible to realize another embodiment in which switching is effected between a plurality of (at least two) operation modes based on the sucked-in air temperature T1 and the sucked-in air humidity H1. Further, the installation positions of the temperature sensor and the humidity sensor of the embodiments may be changed so long as they help them to achieve their object. That is, the above embodiments have been described in order to facilitate the understanding of the present invention, and the above-described structures should not be construed restrictively.

REFERENCE SIGNS LIST

-   1 Air compressor -   10 Compressor main body (first oil temperature adjustment means) -   10 a Compression chamber -   10 b Motor -   10 c Bearing portion -   10 d Bearing portion oil supply port -   10 e, 10 f Compression chamber oil supply port -   20 Oil separator -   21 Discharged air cooling heat exchanger -   22 Oil cooling heat exchanger -   23 Blower (second oil temperature adjustment means) -   31 Sucked-in air temperature sensor (sucked-in air temperature     detection means) -   32 Sucked-in air humidity sensor (sucked-in air humidity detection     means) -   34 Oil temperature sensor -   50 Airflow -   51 Oil flow rate control valve (third oil temperature adjustment     means) 

1. An air compressor comprising: a compressor main body; a compression chamber of the compressor main body compressing sucked-in air; an oil supply port supplying a lubricating oil to the compression chamber; an oil separator separating compressed air discharged from the compression chamber and the lubricating oil from each other; oil temperature adjustment means adjusting temperature of the lubricating oil supplied to the oil supply port; control means controlling the oil temperature adjustment means; sucked-in air temperature detection means detecting temperature of the sucked-in air; and sucked-in air humidity detection means detecting humidity of the sucked-in air, wherein the control means controls the oil temperature adjustment means on the basis of detection information of the sucked-in air temperature detection means and the sucked-in air humidity detection means.
 2. The air compressor according to claim 1, wherein the oil temperature adjustment means is controlled such that temperature of the lubricating oil supplied to the oil supply port rises in a case where temperature of the sucked-in air detected by the sucked-in air temperature detection means is substantially fixed and humidity of the sucked-in air detected by the sucked-in air humidity detection means rises.
 3. The air compressor according to claim 1, further comprising: an oil cooling heat exchanger cooling the lubricating oil; and a blower sending air to the oil cooling heat exchanger, wherein the oil temperature adjustment means is at least one of the compressor main body and the blower.
 4. The air compressor according to claim 3, further comprising: a flow path toward the oil cooling heat exchanger on downstream side of the oil separator; and a bypass flow path joining the flow path after bypassing the oil cooling heat exchanger, wherein the bypass flow path includes an oil flow rate control valve controlling flow rate of the lubricating oil.
 5. The air compressor according to claim 1, further comprising: oil temperature detection means detecting temperature of the lubricating oil supplied to the oil supply port, wherein a target temperature is calculated from a lubricating oil temperature detected by the oil temperature detection means, a sucked-in air temperature detected by the sucked-in air temperature detection means, and a sucked-in air humidity detected by the sucked-in air humidity detection means; and the oil temperature adjustment means is controlled so as to diminish a difference between the lubricating oil temperature and the target temperature. 